The International Cycling Union on Friday said it will wait for the U.S. Anti-Doping Agency to explain why Lance Armstrong should lose his unprecedented seven Tour de France titles before commenting on the case.

The news preceded a statement from USADA saying it had officially stripped Armstrong of his Tour de France titles after he dropped his fight against drug charges that threatened his legacy as one of the greatest cyclists of all time.

"Any time we have overwhelming proof of doping, our mandate is to initiate the case through the process and see it to conclusion as was done in this case," USADA CEO Travis Tygart said.

The UCI says the World Anti-Doping Code requires USADA to do this in cases "where no hearing occurs."

Amaury Sport Organization, which runs the Tour de France, says it will wait to see what happens before commenting on Armstrong's case.

USADA also said it had issued Armstrong a lifetime ban on Friday. Under the World Anti-Doping Code, he could lose the bronze medal from the 2000 Olympics as well as any awards, event titles and cash earnings.

The UCI and USADA have engaged in a turf war over who had jurisdiction in the case.

Armstrong, who retired last year, declined to enter USADA's arbitration process -- his last option -- because he said he was weary of fighting accusations that have dogged him for years. He consistently has pointed to the hundreds of drug tests that he has passed as proof of his innocence during his extraordinary run of Tour titles from 1999 to 2005.

"There comes a point in every man's life when he has to say, 'Enough is enough.' For me, that time is now," Armstrong said in a statement sent to The Associated Press. He called the USADA investigation an "unconstitutional witch hunt."

"I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999," he said. "The toll this has taken on my family and my work for our foundation and on me leads me to where I am today -- finished with this nonsense."

USADA reacted quickly and treated Armstrong's decision as an admission of guilt, hanging the label of drug cheat on an athlete who was a hero to thousands for overcoming life-threatening testicular cancer and for his foundation's support for cancer research.

"It is a sad day for all of us who love sport and athletes," Tygart said. "It's a heartbreaking example of win at all costs overtaking the fair and safe option. There's no success in cheating to win."

Armstrong disputed USADA's jurisdiction to strip the titles. He insisted that his decision is not an admission of drug use but a refusal to enter an arbitration process he believes is unfair.

"USADA cannot assert control of a professional international sport and attempt to strip my seven Tour de France titles," he said. "I know who won those seven Tours, my teammates know who won those seven Tours, and everyone I competed against knows who won those seven Tours."

Armstrong tweeted Friday that he's still planning to ride in a mountain bike race in Aspen, Colo., on Saturday, and follow it up with a marathon on Sunday.

He tweeted that he was "excited to be racing" and by the 9,000 feet of up and down over 36 miles on Saturday.

Armstrong spokesman Mark Higgins said the races are not governed by USADA.

The races will be Armstrong's first public appearance since the sanctions were handed down. Higgins said Armstrong also plans to deliver a keynote speech at a cancer conference in Montreal on Wednesday.

USADA maintains that Armstrong has used banned substances as far back as 1996, including the blood-booster EPO and steroids as well as blood transfusions -- all to boost his performance.

World Anti-Doping Agency president John Fahey says Armstrong's decision to drop his fight against drug charges was an admission the allegations "had substance in them." Fahey told The Associated Press he was certain USADA acted properly.

"I am confident and WADA is confident that the USADA acted within the WADA Code, and that a court in Texas also decided not to interfere," Fahey said in a telephone interview. "They now have the right to apply a penalty that will be recognized by all WADA Code countries around the world."

Fahey said Armstrong must now live with the consequences of his decision not to continue fighting the allegations.

"He had a right to contest the charges. He chose not to," Fahey said. "The simple fact is that his refusal to examine the evidence means the charges had substance in them. Under the rules, penalties can now be imposed."

When asked whether USADA had the authority to strip Armstrong of his Tour de France titles, Fahey replied: "Olympic medals and titles are for other agencies to decide, not WADA."

In Lausanne, Switzerland, early Friday, International Olympic Committee spokesman Mark Adams said the IOC would have to consider decisions made by USADA and the UCI "before deciding its next steps."

The UCI had backed Armstrong's legal challenge to USADA's authority and in theory could take the case before the international Court of Arbitration for Sport.

"The UCI recognizes that USADA is reported as saying that it will strip Mr. Armstrong of all results from 1998 onwards in addition to imposing a lifetime ban from participating in any sport which recognizes the World Anti-Doping Code," Friday's UCI statement said.

"Article 8.3 of the WADC states that where no hearing occurs the Anti-Doping Organization with results management responsibility shall submit to the parties concerned (Mr. Armstrong, WADA and UCI) a reasoned decision explaining the action taken.

"As USADA has claimed jurisdiction in the case the UCI expects that it will issue a reasoned decision in accordance with Article 8.3 of the Code."

Tygart said UCI was "bound to recognize our decision and impose it" as a signer of the World Anti-Doping Code.

"They have no choice but to strip the titles under the code,"
he said.

Armstrong, 40, walked away from the sport in 2011 without being charged after a two-year federal criminal investigation into many of the same accusations he faces from USADA. The federal probe was closed in February, but USADA announced in June it had evidence Armstrong used banned substances and methods -- and encouraged their use by teammates. The agency also said it had blood tests from 2009 and 2010 that were "fully consistent" with blood doping.

Included in USADA's evidence were emails written by Armstrong's former U.S. Postal Service teammate Floyd Landis, who was stripped of his 2006 Tour de France title after a positive drug test. Landis' emails to a USA Cycling official detailed allegations of a complex doping program on the team.

USADA also said it had 10 former Armstrong teammates ready to testify against him. Other than suggesting they include Landis and Tyler Hamilton, both of whom have admitted to doping offenses, the agency has refused to say who they are or specifically what they would say.

"There is zero physical evidence to support (the) outlandish and heinous claims," Armstrong said. "The only physical evidence here is the hundreds of (doping) controls I have passed with flying colors."

Armstrong sued USADA in Austin, where he lives, in an attempt to block the case and was supported by the UCI. A judge threw out the case Monday, siding with USADA despite questioning the agency's pursuit of Armstrong in his retirement.

"USADA's conduct raises serious questions about whether its real interest in charging Armstrong is to combat doping, or if it is acting according to less noble motives," such as politics or publicity, U.S. District Judge Sam Sparks wrote.

Now the ultracompetitive Armstrong has done something virtually unthinkable for him: He has quit before a fight is over.

"Today I turn the page. I will no longer address this issue, regardless of the circumstances. I will commit myself to the work I began before ever winning a single Tour de France title: serving people and families affected by cancer, especially those in underserved communities," Armstrong said.

Armstrong could have pressed his innocence in USADA's arbitration process, but the cyclist has said he believes most people already have made up their minds about whether he's a fraud or a persecuted hero.

It was a stunning move for an athlete who built his reputation on not only beating cancer but forcing himself through grueling offseason workouts no one else could match, then crushing his rivals in the Alps and the Pyrenees.

Although he already had been crowned a world champion and won individual stages at the Tour de France, Armstrong was relatively unknown in the U.S. until he won the epic race for the first time in 1999. It was the ultimate comeback tale: When diagnosed with cancer, doctors had given him less than a 50 percent chance of survival before surgery and brutal cycles of chemotherapy saved his life.

Armstrong's riveting victories, his work for cancer awareness and his gossip-page romances with rocker Sheryl Crow, fashion designer Tory Burch and actress Kate Hudson made him a figure who transcended sports.

His dominance of the Tour de France elevated the sport's popularity in America to unprecedented levels. His story and success helped sell millions of the Livestrong plastic yellow wrist bracelets and enabled him to enlist lawmakers and global policymakers to promote cancer awareness and research. His Lance Armstrong Foundation has raised nearly $500 million since its founding in 1997.

Foundation chairman Jeffery C. Garvey issued a statement, saying, "Faced with a biased process whose outcome seems predetermined, Lance chose to put his family and his foundation first. The leadership of the Lance Armstrong Foundation remain incredibly proud of our founder's achievements, both on and off the bike."

Armstrong still has the support of Nike, his biggest sponsor and partner in the Livestrong line.

"Lance has stated his innocence and has been unwavering on this position," the company said in a statement. "Nike plans to continue to support Lance and the Lance Armstrong Foundation, a foundation that Lance created to serve cancer survivors."

Created in 2000, USADA is recognized by Congress as the official anti-doping agency for Olympic sports in the United States. Its investigators joined U.S. agents during the federal probe, and Tygart had dismissed Armstrong's lawsuit as an attempt at "concealing the truth." He said the agency is motivated by one goal: exposing cheaters in sport.

Others close to Armstrong were caught up in the charges: Johan Bruyneel, the coach of Armstrong's teams, and three members of the medical staff and a consultant were also charged. Bruyneel is taking his case to arbitration, while two medical team staffers and consulting doctor Michele Ferrari didn't formally contest the charges and were issued lifetime bans by USADA. Ferrari later said he was innocent.

"I'm disappointed for Lance and for cycling in general that things have reached a stage where Lance feels that he has had enough and is no longer willing to participate in USADA's campaign against him," Bruyneel wrote on his personal website.

"Lance has never withdrawn from a fair fight in his life so his decision today underlines what an unjust process this has been."

French legend Laurent Jalabert said he had "mixed feelings" about the decision taken by his longtime rival and Tour de France foe.

"He had a lot of success, a lot of talent and also a way of practicing the sport that not everyone liked," the 1995 Spanish Vuelta winner told Radio TV Luxembourg. "There were people who adored him and people who detested him because he was arrogant, because he loved to win by flattening his rivals. I suppose that some people will like this news, but I am divided over it."

Alberto Contador, who hesitantly partnered with Armstrong during the American's comeback in 2009, says he has not followed the case and "I'm not thinking about it."

The Spanish cyclist, speaking before the start of Friday's seventh stage of the Spanish Vuelta, says Armstrong "always showed such strength, great intelligence and spectacular physical conditioning."

American Century Investments, a company with funds in the Livestrong name, issued a statement Friday through its spokesman, Chris Doyle.

"The USADA may sanction Lance and attempt to strip his titles, but no one can take away what he's done for the 28 million people around the world living with cancer."

In a sport rife with cheaters, Armstrong has been under constant suspicion since the 1990s from those who refused to believe he was a clean rider winning cycling's premier event against a field of doped-up competition.

He had tense public disputes with USADA, the World Anti-Doping Agency, some former teammates and assistants and even Greg LeMond, the first American to win the Tour de France.

Through it all, Armstrong vigorously denied any and all hints, rumors and direct accusations he was cheating. He had the blazing personality, celebrity and personal wealth needed to fight back with legal and public relations battles to clear his name -- and he did, time after time.

Armstrong won his first Tour at a time when doping scandals had rocked the race. He was leading the race when a trace amount of a banned anti-inflammatory corticosteroid was found in his urine; cycling officials said he was authorized to use a small amount of a cream to treat saddle sores.

After Armstrong's second victory in 2000, French judicial officials investigated his Postal Service team for drug use. That investigation ended with no charges, but the allegations kept coming.

Armstrong was criticized for his relationship with Ferrari, who was banned by Italian authorities over doping charges in 2002. Former personal and team assistants accused Armstrong of having steroids in an apartment in Spain and disposing of syringes that were used for injections.

In 2004, a Dallas-based promotions company initially refused to pay him a $5 million bonus for winning his sixth Tour de France because it wanted to investigate allegations raised by media in Europe. Testimony in that case included former teammate Frankie Andreu and his wife, Betsy, saying Armstrong told doctors during his 1996 cancer treatments that he had taken a cornucopia of steroids and performance-enhancing drugs.

Two books published in Europe, "L.A. Confidential" and "L.A. Official," also raised doping allegations, and in 2005, French magazine L'Equipe reported that retested urine samples from the 1999 Tour showed EPO use.

Armstrong fought every accusation with denials and, in some cases, lawsuits against the European media outlets that reported them.

But he showed signs that he was tiring of the never-ending questions. Armstrong retired (for the first time) in 2005 and almost immediately considered a comeback before deciding to stay on the sidelines, in part, because he didn't want to keep answering doping questions.

"I'm sick of this," Armstrong said in 2005. "Sitting here today, dealing with all this stuff again, knowing if I were to go back, there's no way I could get a fair shake -- on the roadside, in doping control, or the labs."

Three years later, Armstrong was 36 and itching to ride again. He came back to finish third in the 2009 Tour de France.

Armstrong raced in the Tour again in 2010, under the cloud of the federal criminal investigation. Early last year, he quit the sport for good, but made a brief return as a triathlete until the USADA investigation shut him down.

During his sworn testimony in the dispute over the $5 million bonus, Armstrong said he wouldn't take performance-enhancing drugs because he had too much to lose.

"(The) faith of all the cancer survivors around the world. Everything I do off the bike would go away, too," Armstrong said then. "And don't think for a second I don't understand that. It's not about money for me. Everything. It's also about the faith that people have put in me over the years. So all of that would be erased."

Information from ESPN Sports Business Insider Darren Rovell, The Associated Press and Efe News Agency was used in this report.